388 Williston — fiTt w Fa mil;/ of Reptiles from the 



fcion distinguishing the head from the tubercle. In Diadeetes, or 

 at least in such species as I have been able to study of this genus, 

 the ribs anteriorly are distinctly double-headed. The transverse 

 processes are short throughout the series, scarcely extending 

 on the sides beyond the margin of the zygapophyses. This 

 character has been given by Case as a distinctive one for his 

 genus Diasparactus, but, in a large species of Diadectes from 

 Texas I do not find any appreciable difference in the promi- 

 nence of the processes, at least in the posterior presacral region. 

 The spines are moderately elongate through the series, thick- 

 ened and somewhat rugose at the upper end. There are large 

 intercentra between the centra below, and as the vertebrae lie 

 in the matrix a considerable space is left between the adjacent 

 vertebrae for cartilage, indicating a very flexible, though not 

 very firm spinal column. The spines, of the posterior part of 

 the column at least, are about one inch in length. The first 

 presacral spine is rather broad and expanded above, the second 

 and more anterior ones are more slender. There is but one 

 sacral vertebra, which has a very broad, stout, sacral rib on 

 each side, turned directly downward so as to cover nearly the 

 whole of the inner side of the ilium at its junction with the 

 ischium and pubis, its antero-posterior width being 60 mm , its 

 vertical width where it joins the ilium, 40 mm . The ribs imme- 

 diately in front and behind are small and slender and do not 

 seem to touch the ilium at all. Case has described Diadectes 

 as having two sacral vertebrae, but in the specimen in the 

 Chicago collections, of a large species, the structure of the 

 sacrum seems to be quite as in Limnoscelis ; and this is also 

 the case in a new genus of Diadectidae, which Professor Case 

 will describe from a specimen in the University of Chicago 

 collections, collected by Mr Miller. 



The first chevron occurs at the hind end of the third caudal 

 vertebra, the first one visible above the ischia from below ; the 

 first three or four of the caudal vertebrae have short, free ribs, 

 as in other genera of American Cotylosauria. The tail, as pre- 

 served in specimen No. 908, is rather slender, with rather 

 short spines and chevrons, rather precluding the idea that the 

 animal was marked natatorial in habit. The terminal vertebrae 

 are a little elongated. 



Pectoral Girdle and Extremity. — The pectoral girdle lies 

 in very orderly arrangement, with little if any distortion. 

 Both clavicles are in articulation with the interclavicle, scap- 

 idae and cleithra. The clavicles have the usual cotylosaurian 

 form, curving under the .anterior end of the interclavicle and 

 the anterior margin of the coracoid, curved and somewhat 

 spoon-shaped below. The long, dilated, scapular part is curved 

 upward in a vertical plane and obliquely backward in the artic- 



